In record media processing machines in which different operations such as reading, sorting and encoding of documents are done on the same machine, the speed of the document being processed must often decrease at the printing station because conventional printers are not capable of matching processing speeds which can be attained by other modules of the machine. An additional transport mechanism may therefore be employed to adjust the document speed, first to the slower printer speed, and then to the normal speed of the machine. This speed variation limits the machine throughput and is a major cause of document jam and edge damage. Also, in order to produce a good quality, high resolution print, such as defined by ABA Standard for E-13B, impact printing with full face characters is normally used. This produces a high acoustical noise level.
A detailed description of the E-13B magnetic ink character recognition font may be found in the "American National Standard Print Specifications for Magnetic Ink Character Recognition" published by American National Standards Institute, Inc., 1430 Broadway, New York, N.Y. 10018.
A typical printer employed in a financial item processing machine may be an impact printer comprising two banks of hammers, placed on the same line. The hammers carry a complete set of full face characters. During a printing operation, a document moves at a constant speed in front of the hammer banks. A hammer having a character symbol "X", for example, will strike to provide an impression of "X" on the document whenever the appropriate location for an "X" in the message, as determined beforehand, appears in the proper position with respect to the hammer bearing the "X" character. In other words, the proper time for the firing of each hammer in such an apparatus is a function of the location of each particular character, as well as a function of the paper speed and position. This dependency makes the control of hammer firing more complex. Furthermore, the speed of the document through the printer is limited by the short contact time between the hammer and the document, as determined by print character smearing, and also by the cycle time of the hammer in the worst-case situation in which a hammer must strike two or more times consecutively. All of these considerations affect the throughput speed of the machine.